1. Field of the Invention
The present invention relates to a plate-link chain, in particular for a belt-driven conical-pulley transmission having a continuously variable transmission ratio, having a large number of link plates pivotally connected with each other via pairs of rocker members that comprise two rocker members each, the rocker members running transverse to the longitudinal direction of the plate-link chain and being situated in openings in the link plates and there being curved contact surfaces situated on the rocker members and the link plates, along which curved surfaces the rocker members and link plates bear against each other to transmit force, and there being curved rolling surfaces situated on the rocker members, along which the rocker members roll on each other and/or slide on each other on pitch lines to transmit force.
2. Description of the Related Art
Such a plate-link chain can be employed for example as a means of transmitting tractive force in a belt-driven conical-pulley transmission for a motor vehicle or the like, and there transmit the tractive force by means of frictional contact between the rocker members and the conical disk surfaces of the two conical disk pairs. The plate-link chain may also be designed as a toothed chain and transmit tractive force from a driving to a driven chain wheel.
A plate-link chain designed as a toothed chain normally has a device for tensioning the toothed chain in the slack strand. This device for tensioning the toothed chain serves for example to prevent pulsating of the toothed chain due to vibration excitation, and also to shape the entry process of the teeth of the toothed chain onto a chain wheel so that tooth skipping is prevented. On the chain wheels the toothed chain is deflected in such a way that the center of curvature of the portion of the toothed chain that is curved in the region of the deflection lies within the closed chain section.
In contrast, when a chain tensioner in the form for example of a chain tensioning bar acts on the back of the link plates, the toothed chain undergoes a curvature that differs from the curvature that occurs in the region of the deflection; the particular portion of the toothed chain which is acted on by the chain tensioner is curved in the opposite direction and the center of curvature of this portion of the toothed chain lies outside of the closed chain section of the plate-link chain. A curvature of this sort is referred to as swing-back.
To limit the deflection angle of the swing-back process for example from the stretched position, in known versions of plate-link chains for belt-driven conical-pulley transmissions and toothed chains there is provision for limiting the swing-back in the joint of the lower zone of an adjacent link plate.
The mode of functioning here is such that a rocker member comes into contact with a region of the lower contact surface of the adjacent link plate. Thus the striking of the rocker member on the contact surface of the adjacent link plate occurs in a zone that is already critically loaded due to the transmission of tensile force from the rocker member to the link plate. Hence in this zone of concentrated tension due to the transmission of tensile force, yet another additional overlay of forces occurs, and thus tensions due to the swing-back protection. In the operation of the toothed chain this can result in increased wear, and ultimately to early fatigue failure. The fatigue strength of the toothed chain is reduced.
Plate-link chains that have become known heretofore had symmetrical rocker members, which were situated in openings in the link plates. These known rocker members are symmetrical in construction in reference to a plane of symmetry that divides the rocker members into an upper and a lower half. As a result of this configuration, a distance from the inner peripheral rim of the opening that receives the rocker members to an outer peripheral edge of the link plate in the region of a so-called lower yoke is made smaller, and thus the cross sectional region available for transmitting force is reduced in size.
In consequence, a concentration of tension appears in this region between the opening of the link plate and the edge of the link plate, which ultimately results in a reduction of the service life and of the force transmitting capability of the plate-link chain. To counter this problem, a plate-link chain has already become known which has asymmetrical rocker members in the direction of the rocker member height and thereby makes sure that the workpiece stresses which arise in the upper and lower contact surface regions between rocker member and link plate are significantly reduced, so that the service life of the chain increases as a result.
With a plate-link chain of this sort it is significant that the asymmetrical rocker members are inserted into the openings in the link plates in the correct orientation, since otherwise the pitch surfaces of the rocker members that are intended for transmitting force cannot roll on each other as intended, with the consequence that jamming of the rocker members in the opening can occur, and thus a malfunction that may result in failure of the plate-link chain.
To achieve this correct orientation of the rocker members in the openings of the link plates, a plate-link chain has already become known on the basis of unpublished German patent application DE 10 2005 061 081.1, owned by the assignee of the present application, whose link plates have a region that is bowed (curved) in an inward direction, so that if the rocker members are oriented incorrectly an overlapping of the outer contour of the rocker members with the inside contour of the opening occurs in the link plates, so that the rocker member which is not installed in the correct orientation can no longer be inserted into the opening of the link plate, and in this way erroneous installation of the rocker members in the openings of the link plates is avoided.
It has been found that this known plate-link chain already provides an improvement compared to the plate-link chain described above, in regard to additional tension on the tension-critical zone in the region of the lower yoke of the link plate. But even this known plate-link chain has room for improvement in regard to the stress in the described tension-critical zone due to the striking of the rocker member on a contact surface of an adjacent link plate to protect against swing-back.
Starting from this point, an object of the present invention is now to refine the known plate-link chain in such a way that the force applied to the plate-link chain due to the striking of the rocker member on the link plate to limit the swing-back angle takes place in a less tension-critical zone along the opening of the link plate.